The fire erupted around 4:50 a.m. on the sixth floor of the seven-story apartment building.Demetrius E. Loadholt

A financially troubled Queens man butchered his wife and their teen son to death with a knife before setting them on fire and killing himself in a grisly murder-suicide, sources said.

The gruesome scene was discovered when firefighters arrived to the family’s home at The Blair House on Roosevelt Avenue in Flushing just before 5 a.m. Tuesday and found the three bodies inside the fully engulfed living room of their sixth floor apartment.

Investigators believe Korea native Joon Lee 50, snapped early Tuesday and repeatedly stabbed his wife and their 16-year-old son before stacking the bodies on top of one another and dousing them in gasoline.

Lee then set ablaze the corpses of his wife and son before slashing his wrists.

It took 12 FDNY units and 60 firefighters a little more than 30 minute to get the fire under control, officials said.

Once extinguished, police entered the house of horrors and began piecing together the puzzle.

“There are knife wounds, so many we can’t tell how many because of the fire,” a source said.

Investigators also found a note penned by the dad somewhere in the blood soaked, burned our home that described the family’s money woes and how Joon was struggling to find work. sources said.

A family friend told police that Joon had begun acting erratically the last time they had seen each other.

“He told us the last time they were together the father was drinking and banging his head against a wall,” said a source. “He said the father would go a little nuts sometimes.

A family friend identified the mother as Sung Lee, a 56-year-old nail salon worker and the son as 16-year-old Brooklyn Technical High School student Brian Lee.

Longtime neighbor Lo Lee, who is not related to the victims, said he heard a disturbance coming from next door early Tuesday

“[I] heard loud banging,” Lee said through a translator. “[I thought I heard] a gunshot and then another gunshot.”

Lee didn’t venture out of his apartment until well after the flames had been extinguished and said he took a peek through the open door where police were investigating the brutal slayings.

“[I] looked inside and saw blood on the floor, on the back of the door, blood in the hallway,” he said.

“The son was laying on top of the mom,” he continued. “The man was slit his wrists.”

Faculty at Brooklyn Tech High School broke the sad news to Brian’s distraught classmates, telling them only that he had died in a fire and sparing them the horrible details.

A classmate said Brian was a electromechanic major and played the trumpet.

“He was a good kid,” the student said.

The tragedy happened just blocks from where another man, Xie Bin, 51, fatally shot his girlfriend, Ya Ling Meng, 46, in the head before turning the weapon on himself Monday night.

Assemblyman Ron Kim said the timing of the event is especially unfortunate because this is supposed to be a happy time for the Korean people.

“Yesterday was the Chuseok festival, which is the largest thanks giving festival for Korean families,” he said. “Its a time to get together with family and like any holiday, there is a heightened suicide rate. It can be more depressing during this time.”